435 research outputs found
Optical detection of a BCS phase transition in a trapped gas of fermionic atoms
Light scattering from a spin-polarized degenerate Fermi gas of trapped
ultracold Li-6 atoms is studied. We find that the scattered light contains
information which directly reflects the quantum pair correlation due to the
formation of atomic Cooper pairs resulting from a BCS phase transition to a
superfluid state. Evidence for pairing can be observed in both the space and
time domains.Comment: 8 pages, 4 figures, revte
1D to 3D Crossover of a Spin-Imbalanced Fermi Gas
We have characterized the one-dimensional (1D) to three-dimensional (3D)
crossover of a two-component spin-imbalanced Fermi gas of 6-lithium atoms in a
2D optical lattice by varying the lattice tunneling and the interactions. The
gas phase separates, and we detect the phase boundaries using in situ imaging
of the inhomogeneous density profiles. The locations of the phases are inverted
in 1D as compared to 3D, thus providing a clear signature of the crossover. By
scaling the tunneling rate with respect to the pair binding energy, we observe
a collapse of the data to a universal crossover point at a scaled tunneling
value of 0.025(7).Comment: 5 pages, 4 figure
Dissociation of one-dimensional matter-wave breathers due to quantum many-body effects
We use the ab initio Bethe Ansatz dynamics to predict the dissociation of
one-dimensional cold-atom breathers that are created by a quench from a
fundamental soliton. We find that the dissociation is a robust quantum
many-body effect, while in the mean-field (MF) limit the dissociation is
forbidden by the integrability of the underlying nonlinear Schr\"{o}dinger
equation. The analysis demonstrates the possibility to observe quantum
many-body effects without leaving the MF range of experimental parameters. We
find that the dissociation time is of the order of a few seconds for a typical
atomic-soliton setting.Comment: The final version, contains supplemental material, PRL (in press),
see
https://journals.aps.org/prl/accepted/71072YefTec1c16a44807625d0168f716b918fab
Enlarging and cooling the N\'eel state in an optical lattice
We propose an experimental scheme to favor both the realization and the
detection of the N\'eel state in a two-component gas of ultracold fermions in a
three-dimensional simple-cubic optical lattice. By adding three compensating
Gaussian laser beams to the standard three pairs of retroreflected lattice
beams, and adjusting the relative waists and intensities of the beams, one can
significantly enhance the size of the N\'eel state in the trap, thus increasing
the signal of optical Bragg scattering. Furthermore, the additional beams
provide for adjustment of the local chemical potential and the possibility to
evaporatively cool the gas while in the lattice. Our proposals are relevant to
other attempts to realize many-body quantum phases in optical lattices.Comment: 8 pages, 10 figures (significantly revised text and figures
Growth and Collapse of a Bose Condensate with Attractive Interactions
We consider the dynamics of a quantum degenerate trapped gas of Li-7 atoms.
Because the atoms have a negative s-wave scattering length, a Bose condensate
of Li-7 becomes mechanically unstable when the number of condensate atoms
approaches a maximum value. We calculate the dynamics of the collapse that
occurs when the unstable point is reached. In addition, we use the quantum
Boltzmann equation to investigate the nonequilibrium kinetics of the atomic
distribution during and after evaporative cooling. The condensate is found to
undergo many cycles of growth and collapse before a stationary state is
reached.Comment: Four pages of ReVTeX with four postscript figure
Deformation of a Trapped Fermi Gas with Unequal Spin Populations
The real-space densities of a polarized strongly-interacting two-component
Fermi gas of Li atoms reveal two low temperature regimes, both with a
fully-paired core. At the lowest temperatures, the unpolarized core deforms
with increasing polarization. Sharp boundaries between the core and the excess
unpaired atoms are consistent with a phase separation driven by a first-order
phase transition. In contrast, at higher temperatures the core does not deform
but remains unpolarized up to a critical polarization. The boundaries are not
sharp in this case, indicating a partially-polarized shell between the core and
the unpaired atoms. The temperature dependence is consistent with a tricritical
point in the phase diagram.Comment: Accepted for publication in Physical Review Letter
The Superfluid State of Atomic Li6 in a Magnetic Trap
We report on a study of the superfluid state of spin-polarized atomic Li6
confined in a magnetic trap. Density profiles of this degenerate Fermi gas, and
the spatial distribution of the BCS order parameter are calculated in the local
density approximation. The critical temperature is determined as a function of
the number of particles in the trap. Furthermore we consider the mechanical
stability of an interacting two-component Fermi gas, both in the case of
attractive and repulsive interatomic interactions. For spin-polarized Li6 we
also calculate the decay rate of the gas, and show that within the mechanically
stable regime of phase space, the lifetime is long enough to perform
experiments on the gas below and above the critical temperature if a bias
magnetic field of about 5 T is applied. Moreover, we propose that a measurement
of the decay rate of the system might signal the presence of the superfluid
state.Comment: 16 pages Revtex including 10 figures, submitted to Phys. Rev.
Extreme tunability of interactions in a Li Bose-Einstein condensate
We use a Feshbach resonance to tune the scattering length a of a
Bose-Einstein condensate of 7Li in the |F = 1, m_F = 1> state. Using the
spatial extent of the trapped condensate we extract a over a range spanning 7
decades from small attractive interactions to extremely strong repulsive
interactions. The shallow zero-crossing in the wing of the Feshbach resonance
enables the determination of a as small as 0.01 Bohr radii. In this regime,
evidence of the weak anisotropic magnetic dipole interaction is obtained by
comparison with different trap geometries
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